1. Field of the Invention
This invention relates to rubber compositions suitable particularly for adhesion to hydrogenated rubbers and also to metallic and fibrous materials.
2. Prior Art
Generally, rubber products including tires, belts, molded articles, rubber rolls, hoses and the like are exposed to elevated temperature and heavy load when applied to automotive vehicles, construction machinery or hydraulic devices. Such rubber products therefore should be highly resistant to heat and oil over prolonged periods of time.
Various rubbers have been proposed which are resistant to oils and high temperatures of 120.degree.-150.degree. C., and they include acrylonitrile-butadiene copolymer rubber (NBR), acrylic rubber (ACM), ethylene-acrylic copolymer rubber (AEM), ethylene-acrylic-vinyl acetate terpolymer rubber (ER), chlorosulfonated polyethylene rubber (CSM), chlorinated polyethylene rubber (CM) and acrylonitrile-butadiene copolymer rubber having its conjugated dienes rearranged by hydrogenation (hydrogenated NBR). These known high-performance rubbers are in many instances used as composite structures made up of reinforcing metals such particularly as brass and fibers.
Sulfur is known to facilitate the adhesion of rubbers to brass and fiber. The high-performance rubber however when sulfur-vulcanized fails to fully exhibit its heat resistance, leading to quality deterioration. Non-sulfur vulcanization, gives adequate heat resistance, but is literally unsatisfactory in respect of adhesion to brass and fiber.
To improve both heat resistance and adhesion to metal and to fiber, a certain metal- or fiber-adhesive intermediate rubber is usually interposed between the high-performance rubber and the reinforcing material. Most thermally resistant among the aforementioned high-performance rubbers is hydrogenated NBR rubber which however calls for vulcanization with an organic peroxide. This rubber so vulcanized is effective for adhesion to peroxide-vulcanized rubbers but not to brass or to fiber. Sulfur-vulcanized rubbers are good for brass and fiber, but often induce interfered vulcanization reaction when contacted with peroxide-vulcanized hydrogenated NBR rubber.
Hydrogenated NBR rubber may be composed of peroxide and sulfur so as to provide balanced heat resistance and adhesion qualities. This type of composition is adhesive only to a limited extent, involving interfered reaction between the two systems of vulcanization, hence deteriorated resistance of the vulcanizate to brittle fracture under external forces applied as by dynamic vibration. Thus, there has arose an urgent need for an improved rubber composition which is capable of rendering hydrogenated NBR rubber feasible where they must be used in combination with brass and fiber.